Numerical Analysis of Mixing Performance in an Electroosmotic Micromixer with Cosine Channel Walls

Abstract

Micromixers have significant potential in the field of chemical synthesis and biological pharmaceuticals, etc. In this study, the design and numerical simulations of a passive micromixer and a novel active electroosmotic micromixer by assembling electrode pairs were both presented with a cosine channel wall. The finite element method (FEM) coupled with Multiphysics modeling was used. To propose an efficient micromixer structure, firstly, different geometrical parameters such as amplitude-to-wavelength ratio (a/c) and mixing units (N) in the steady state without an electric field were investigated. This paper aims to seek a high-quality mixing solution. Therefore, based on the optimization of the above parameters of the passive micromixer, a new type of electroosmotic micromixer with an AC electric field was proposed. The results show that the vortices generated by electroosmosis can effectively induce fluid mixing. The effects of key parameters such as the Reynolds number, the number of electrode pairs, phase shift, voltage, and electrode frequency on the mixing performance were specifically discussed through numerical analysis. The mixing efficiency of the electroosmotic micromixer is quantitatively analyzed, which can be achieved at 96%. The proposed micromixer has a simple structure that can obtain a fast response and high mixing index.

Keywords: electroosmotic; micromixer; mixing performance; numerical simulation.

Figure 1

The schematic diagram of the proposed micromixers: (a) the passive micromixer design, (b) the distribution of electrodes in the active electroosmotic micromixer.

Figure 2

The step function of the concentration distribution on the microchannel inlet.

Figure 3

Grid system profiles: (a) unstructured triangular mesh, (b) comparison of the mixing efficiency for different grid systems.

Figure 4

The effect of the amplitude-to-wavelength ratio: (a) distributions of concentration surface along the micromixer for the different amplitude-to-wavelength ratios (a/c), (b) the mixing index at the outlet for different values of amplitude-to-wavelength ratios (a/c).

Figure 5

Variations of the mixing quality at the outlet with different mixing units: (a) the mixing index of different amplitude to wavelength ratios, (b) the mixing concentration at the outlet.

Figure 6

Model validation based on Siyue Xiong et al. [33] (a) comparison of the mixing index for different Re numbers, (b) comparison of the mixing index for different voltages.

Figure 7

Simulation of the electroosmotic micromixer: (a) distribution of concentration surface along the micromixer, (b) electric potential streamlines when time t = 1 s, phase shift of pi/4, U₀ = 0.1 mm/s, V₀ = 2 V, f = 5 Hz.

Figure 8

Comparison of the mixing efficiency at the outlet of the proposed micromixer under an AC electric field and a DC electric field with U₀ = 0.1 mm/s, V₀ = 4 V, f = 5 Hz.

Figure 9

Distributions of concentration surface from the A-A section to the outlet of the micromixer for different inlet velocities when time t = 10 s, phase shift of pi/4, V₀ = 2 V, and f = 5 Hz.

Figure 10

Variations of the mixing index at the outlet of the passive micromixer and the electroosmotic micromixer with different Reynolds numbers: (a) the mixing index of the passive micromixer of six amplitude of wavelength ratios, (b) the mixing index of the electroosmotic micromixer within 0–10 s.

Figure 11

Distributions of electrode pairs positions: (a) one pair, (b) two pairs, (c) three pairs, (d) four pairs.

Figure 12

The effect of the number of electrode pairs: (a) distributions and streamlines of concentration surface along the micromixer for different electrode pairs, (b) the mixing index at the outlet for different electrode pairs within 0–20 s when phase shift of pi/4, U₀ = 0.1 mm/s, V₀ = 2 V, and f = 5 Hz.

Figure 13

The effect of phase shift: (a) distributions of concentration surface along the micromixer for different phase shifts, (b) the mixing index at the outlet for different phase shifts within 0–20 s when four pairs of electrodes, U₀ = 0.1 mm/s, V₀ = 2 V, and f = 5 Hz.

Figure 14

The effect of the voltage: (a) distributions of concentration surface along the micromixer for four values of voltage, (b) the mixing index at the outlet for different voltages within 0–35 s with four pairs of electrodes, and a phase shift of pi/4, U₀ = 0.1 mm/s, V₀ = 2 V, and f = 5 Hz.

Figure 15

The effect of the frequency:(a) distributions of concentration surface along the micromixer for different frequencies, (b) the mixing index at the outlet for different frequencies within 0-20 s with four pairs of electrodes and a phase shift of pi/4, U₀ = 0.1 mm/s, and V₀ = 2 V.